In the dose-expansion phase: histologically- or cytologically-confirmed advanced or metastatic biliary tract cancer (BTC), esophagus cancer(EC) (squamous cell carcinoma) or squamous cell carcinoma of the head and neck (SCCHN). - men or women. - Eastern Cooperative Oncology Group (ECOG) status of 0 or 1. - Adequate organ and marrow function. - Subjects must have at least 1 measurable lesion. - Available archived tumor tissue sample. - Willingness to provide consent for biopsy samples.